Characteristic Chemical Profile of Particulate Matter (PM_2.5)—A Comparative Study Between Two Periods, Case Study in Medellín, Colombia

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Comments are detailed in the attached file.

Comments for author File: Comments.pdf

Author Response

1. Recommendation

Major Revision

 

            A: We would like to thank the first reviewer, whose list we are responding to in this document, as well as the other reviewers, whose valuable contributions we have analyzed and considered in our manuscript. As a brief summary of the changes made to our document, we highlight the following:

 

1. We improved the English wording by correcting grammatical and formal errors.
2. We changed some figures to have a greater color contrast, which allows for better visualization of the parameters represented in each figure.
3. We expanded the specificity of the methodological procedures by adding data on the standards and accredited laboratories in which we perform the analytical procedures and sample handling procedures.
4. We expanded the introduction and discussion by orienting the state of the art toward previous studies in which similar analyses have been performed and contrasting the implementation of public policies with reductions in atmospheric contaminant levels.

2.1.   Major comments: 

1. Inclusion of 5 concentrations from the three locations in the abstract will enhance the comprehension of the variations in particulate matter levels.

            A: We have added to the abstract the average PM2.5 concentration values in urban areas, which show the decrease in pollution levels between the first and second periods.

 

2. Introducing chemical symbols at the beginning is crucial for enabling their effective use later in the document.

            A: We made sure that the symbol for each chemical species was defined from the first time it appeared in the manuscript.

 

3. It is crucial to include the findings directly in the text rather than relying on the reader to interpret them from the figures.

            A: we have added more context to the graphs so that the main findings that we want to extract from each of the graphical resources that we present can be more easily evidenced.

 

4. Standardize the sizes of the charts presented in Figures 3 and

            A: In Figures 3 and 4, the diameter of each pie chart corresponds to the average PM2.5 concentration at each station. Therefore, standardizing the sizes would mean the loss of a graphical resource that allows to quickly identify the points with higher pollution levels. It also allows us to observe the changes between the two periods. Therefore, we believe that both figures should be maintained. However, we understand that this may not be an interpretation that is easily appreciated, so we have added a note to the titles of both figures specifically indicating that the size of the graphs is related to the average concentration of the pollutant.

 

5. The findings are not correlated with the previous

            A: We have added references about previous studies in other regions of the world in which reductions in pollutant levels were related to public policies. On the other hand, we expanded the discussion on this topic and identified other studies in Colombia and other regions that have characterized the profiles of PM, especially the fractions of ions, metals, and carbonaceous species. It is important to note that we believe our findings align with previous studies. However, as mentioned above, it is now clearer to readers. The added information on this topic can be found in lines 97-101 and 371-391.

6. A section addressing "Quality Control and Assurance" is essential for the research to ensure that the methodologies and outcomes of the study meet the highest standards of reliability and

            A: we have increased the specificity when writing the methodological parameters by which we assure the quality control of the samples and analyses used in our study, for this we have included information of the laboratories that performed the analytical procedures, the standard methods and international norms that we follow. This information was added in the text of sections 2.2 and 2.3 between lines 147-151; 165-169 and 188-201.

2.2   Minor comments: 

1. Title Page: The title words must be displayed in uppercase

            A: We have displayed the words in uppercase.

 

2. Title Page: Line 15: Rewrite the sentence to be “The region is characterized”

            A: We have rewritten the sentence.

 

3. Title Page: Line 20: Use the plural “analyses” instead of “analysis”

            A: We have corrected the sentence.

 

4. Title Page: Line 22: Rewrite the sentences to be “the two periods”

            A: We have corrected the sentence.

 

5. Title Page: Line 27: Spelling mistake; the word "factions" should be “fractions”

            A: We have corrected the word.

 

6. Title Page: Lines 36- 39: Rewrite the sentences to enhance clarity and comprehension. Suggestion: Air pollution is related to rapid economic and infrastructure growth, particularly in nations and urban areas experiencing rapid This phenomenon is primarily driven by increased resource consumption, which in turn leads to a greater quantity of emissions.

            A: We have rewritten the sentence.

 

7. Title Page: Line 40: Add conjunctions “as” and “both” for the phrase “as emissions from both internal”

            A: We have added the conjunctions.

 

8. Page 2: Lines 42- 46: Rewrite the sentences to enhance clarity and comprehension. Suggestion: The dynamics of atmospheric pollutants are influenced by atmospheric conditions, including factors such as wind speed and direction, as well as phenomena like thermal inversion. Additionally, circulation patterns can lead to the accumulation of pollutants in specific areas, which is frequently observed in valleys or urban areas where the dispersion of these pollutants is more

            A: We have rewritten the sentences.

 

9. Page 2: Lines 52- 53: Employ the appropriate prepositions within the sentence Use “with a reduction in visibility” instead of “with a reduction of the visibility”

            A: We have corrected the structure.

 

10. Page 2: Line 57: Use the right form of the verb; “remains” instead of “remain”

            A: We have corrected the verb.

 

11. Page 2: Lines 67- 81: Rewrite the sentences to enhance clarity and This section has several grammatical errors, such as using erroneous propositions. It is essential to introduce chemical symbols at the outset to facilitate their subsequent use throughout the text.

            A: We have corrected the text for a better understanding.

 

12. Page 2: Lines 82- 96: Utilize concise sentences can enhance

            A: We have corrected the text for a better understanding.

 

13. Page 2: Lines 97- 98: Rewrite the sentences to enhance clarity and comprehension; “The present study evaluated two periods (2014-15 and 2018-19) during which we performed the characterization of PM5 in different zones of Medellín and nearby cities.”

            A: We have corrected the sentence

 

14. Page 2: Lines 103- 104; 122- 133: Rewrite the sentences to enhance clarity and

            A: We have rewritten the sentences enhancing clarity and comprenhension.

 

15. Page 11: Lines 115- 116; 132: Consider the right use of punctuation marks and use the correct letter case.

            A: We have corrected the use of punctuation marks.

16. Page 11: Line 119: Use the proper preposition; a instead of as

            A: We have corrected the preposition.

17. Page 5: Line 167: Correct the spelling mistake; Transmittance instead of Tramitance

            A: We have corrected the spelling mistake

18. Page 5: Lines 189- 191: Including chemical symbols at the beginning for their successful use later in the paper.

            A: We have included the chemical symbols.

19. Page 6: Line 203: Change the word particle to station

            A: We have changed the word.

20. Page 6: Lines 204- 212: Rewrite this section to enhance clarity and comprehension. Employ the appropriate verb forms, prepositions, and punctuation marks within the sentence structure.

            A: We have rewritten the section.

21. Page 7: Line 215 and 218: Correct the spelling mistake; parentheses instead of parenthesis

            A: We have corrected the words.

22. Page 8: Line 240: Use the proper verb form and

            A: We have changed “in the Figure 5 is marked” for “Figure 5 highlights”.

23. Page 11: Line 372: Remove the duplicated word.

            A: We have removed the duplicated word

Reviewer 2 Report

Comments and Suggestions for Authors

The article is focused on understanding PM2.5 concentration variations across polluted cities in south Africa. The article also suggests the effect of policy changes that contribute to the differences in concentration of pollutants with time. Authors use well established compositional analysis tools to understand the source of PM2.5 along with their correlation with rural or urban sites. The article is well written with assumptions and experimental approach clearly defined. The article is easy to read and digest and the data supports the results and inferences drawn.

 

I have a few concerns about the article that are outlined as following:

 

• Sample Collection: In experimental studies, enough details should be provided to ensure researchers can attempt to replicate the work in future. The authors also mention- size selective inlet-Gravimetric method for high volume sampler. It would be useful for readers to know the cutoff size of their samplers for both high and low volume sampling. Other experimental details are provided with sufficient resolution to allow replication of research in future for interested researchers.
• Authors state that metals occupy less than 10% of PM2.5 mass, but included important toxic species. Authors report light to heavy metals present in the sample. Elements such as Na, Si, Ca could be from sources of mineral dust but discussion about these are not present.
• In pie Charts, it is difficult to interpret the graphs due to colors being similar shades of blue. I would recommend either shading them with same color but different patterns so that color variations could be avoided or choosing colors with extreme contrasts.
• Since authors mention that OC/EC ratio has variations that could be because different sources influence each location differently. Can authors tie these conclusions to policy implementation?
• Since authors mention in discussion that the changes in fuel(diesel) quality could have impacted the sulfate concentration, it will be helpful if graphs/data can be provided in main text showing the distribution of anions [SO4-3 > NO-3 > Cl- > Fl- ] in samples along with their variations over period to support this claim.

Author Response

We would like to thank you for your valuable comments on our manuscript, we have considered them and you will find our response below.

 

Sample Collection: In experimental studies, enough details should be provided to ensure researchers can attempt to replicate the work in future. The authors also mention- size selective inlet-Gravimetric method for high volume sampler. It would be useful for readers to know the cutoff size of their samplers for both high and low volume sampling. Other experimental details are provided with sufficient resolution to allow replication of research in future for interested researchers.

A: We have added information on how to cut the filter, the dimensions of the filter and the extraction method. Lines 165-169;

Authors state that metals occupy less than 10% of PM2.5 mass, but included important toxic species. Authors report light to heavy metals present in the sample. Elements such as Na, Si, Ca could be from sources of mineral dust but discussion about these are not present.

A: Although other sections of the document mention that sources of PM are both natural and antrophogenic, we have added a clarification to this paragraph to indicate that these compounds also apply to natural sources.Lines 266-268.

In pie Charts, it is difficult to interpret the graphs due to colors being similar shades of blue. I would recommend either shading them with same color but different patterns so that color variations could be avoided or choosing colors with extreme contrasts.

A: We have changed the colour palette in graphics 3, 4 and 5.

Since authors mention that OC/EC ratio has variations that could be because different sources influence each location differently. Can authors tie these conclusions to policy implementation?

A: In our conclusions on the study, we have stated that although the implementation of the policies has been a key factor in the proven reduction in pollution levels, other different factors such as climatology, morphology, oscillations, etc. may have influenced and the direct effects are outside the scope of this research. However, we have seen that the levels are very different when comparing rural and urban areas, finding different values of the OC/EC ratio between periods, with an increase in this ratio on the second period, which we believe is more related to the contribution of fires inside and outside the study area. We have discussed the above in lines 358-370.

Since authors mention in discussion that the changes in fuel(diesel) quality could have impacted the sulfate concentration, it will be helpful if graphs/data can be provided in main text showing the distribution of anions [SO4-3 > NO-3 > Cl- > Fl- ] in samples along with their variations over period to support this claim.

A: We have discussed the above, including the arguments between lines 351-357.

Reviewer 3 Report

Comments and Suggestions for Authors The study conducted during the two periods 2014-2015 and 2018-2019 in Medellin -Colombia, evaluates the characteristic chemical profile of PM 2.5 in a region of approximately 376 km² with a population of over 2.5 million inhabitants of which 305 represent the urban area. The results suggest a reduction in the levels of this pollutant between the periods, however, above the values ​​recommended by the WHO regarding air quality. The policies and actions implemented to reduce pollutant emissions are correlated with the evident reduction of pollutants, but it is important to take into account variables related to climatic variations, meteorological conditions or depression dynamics. The samples were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) in a Thermo Scientific model I CAP-RQ instrument, using reference protocols and methods. The concentrations of ions (SO42-, NO3-, F- and Cl-) in PM2.5 were determined by ion chromatography using the standard reference method in a Thermo Scientific reference Dionex Aquion instrument. Ambient organic carbon (OC) and elemental carbon (EC) are analyzed in PM2.5. The samples were collected in quartz fiber filters, by continuous temperature combustion in oxidizing and/or non-oxidizing atmospheres. The data were statistically analyzed and presented in graphs and tables.

Author Response

We would like to thank you for your valuable comments on our manuscript, we have considered them and you will find our response below.

The policies and actions implemented to reduce pollutant emissions are correlated with the evident reduction of pollutants, but it is important to take into account variables related to climatic variations, meteorological conditions or depression dynamics.

A: We have discussed the above, including the arguments between lines 371-376.

Reviewer 4 Report

Comments and Suggestions for Authors

Medellín, a densely populated city in the Colombian Andes faces significant health and envi-ronmental risks due to poor air quality. This is linked to the atmospheric dynamics of the valley in which it is located (Aburrá Valley). This is a region characterized by being a narrow valley and one of the most polluted regions in South America. This is a comparative study of the chem-ical composition of PM2.5 in Medellín between two periods (2014-15 and 2018-19) in which tem-poral trends and emission sources were evaluated. PM2.5 samples were collected from urban, suburban and rural stations following standardized protocols and compositional analysis of metals (ICP-MS), ions (ion chromatography) and carbonaceous species (OC and EC by ther-mo-optical methods) were performed. The results show a reduction in average PM2.5 concentra-tions between periods, although levels are still above WHO guidelines. Urban stations showed higher PM2.5 levels, with predominance of carbonaceous aerosols (TC = OC + EC = 35-50% of PM2.5 mass) and secondary ions (sulfate > nitrate, 13-14% of PM2.5 mass). Rural areas showed lower PM2.5 concentrations but elevated OC/EC ratios, suggesting the influence of biomass burning as a major emission source. Metals were found to occupy factions of less than 10% of the PM2.5 mass, however, included important toxic species associated with respiratory and cardio-vascular risks. This study highlights progress in reducing PM2.5 levels in the region which has been impacted by local policies, but emphasizes current and future challenges related mainly to secondary aerosol formation and carbonaceous aerosol emissions. It is interesting and it is relevant and within the scope of the journal.

The paper has certain novelty and advantages for this field research work, and has value for publishing in the Journal. Therefore, I suggest that this paper be accepted with further modification.

1 Table 3. (Mean concentration of the analyzed species) should be revised to Table 2

2There should be some new references.

 [1]Change in Air Quality during 2014–2021 in Jinan City in China and Its Influencing Factors. Toxics, 2023 11, no. 3: 210. https://doi.org/10.3390/toxics11030210

[2] A Hybrid Wavelet-Based Deep Learning Model for Accurate Prediction of Daily Surface PM2.5 Concentrations in Guangzhou City. Toxics. 2025; 13(4):254. https://doi.org/10.3390/toxics13040254

3. Through further proofreading, the quality of this article should be greatly improved.

Author Response

We would like to thank you for your valuable comments on our manuscript, we have considered them and you will find our response below.

Table 3. (Mean concentration of the analyzed species) should be revised to Table 2

A: We have corrected the error in the table nomenclature.

There should be some new references.

[1] Change in Air Quality during 2014–2021 in Jinan City in China and Its Influencing Factors. Toxics, 2023 11, no. 3: 210. https://doi.org/10.3390/toxics11030210

[2] A Hybrid Wavelet-Based Deep Learning Model for Accurate Prediction of Daily Surface PM2.5 Concentrations in Guangzhou City. Toxics. 2025; 13(4):254. https://doi.org/10.3390/toxics13040254

A: We have added the references
[84] Change in Air Quality during 2014–2021 in Jinan City in China and Its Influencing Factors. Toxics, 2023 11, no. 3: 210. https://doi.org/10.3390/toxics11030210

[32] A Hybrid Wavelet-Based Deep Learning Model for Accurate Prediction of Daily Surface PM2.5 Concentrations in Guangzhou City. Toxics. 2025; 13(4):254. https://doi.org/10.3390/toxics13040254          

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

-

Comments on the Quality of English Language

-